This invention has to do with a method and apparatus for tensioning coiled springs that are usually mounted upon a central shaft and is specifically directed to a coiled spring that is mounted on a fixed shaft and used in providing the proper counterbalancing tension for use with overhead garage door openers.
The installation of overhead garage doors usually involves installing railings that support each side of the door and upon which the sides of the door are freely slideable. The railings usually have three sections which comprise an upper section in an horizontal position for storing the door in an open position, a vertical section for holding the door in a closed position, and a curved section for transition of the sides of the door from the horizontal rails to the vertical rails. As most garage doors are too heavy for a normal person to lift some sort of counterbalancing mechanism is usually provided so that the full weight of the door is not encountered when the door is transferred to the vertical sections of the railings when one closes the garage door. Even with power operated door opener devices a counter balance mechanism is provided so as to be able to reduce the horsepower requirements of the drive motor. For safety reasons the counter balancing mechanisms are also necessary in the event of failure of the garage door openers.
A prevailing type of counterbalancing mechanism in wide use with such overhead garage door openers, especially ones that have power operated motors to assist the opening and closing of the doors, is a coiled spring mounted upon a rotatable shaft. The shaft is usually located above the opening that is to be covered by the door and is transversely located across the path of the door. Upon this shaft is mounted a coiled spring in a somewhat concentric manner such that the longitudinal centerline of the spring approximately locates upon the longitudinal centerline of the shaft. One end of the spring is fixedly attached to a structure upon which the shaft is rotatably mounted and the other end of the spring is held releasably attached to the rotatable shaft. A cable arrangement is usually attached to the rotatable shaft in such a manner that it may be wound and unwound from the shaft. The other end of the cable is usually attached to the lowermost end of the door. Raising the door is supposed to cause the cable to wind around the shaft and lowering the door is supposed to cause the cable to unwind from the shaft.
The tensioning for the garage door takes the form of adjusting the tension exerted by the coiled spring upon the rotatable shaft that also holds the wound cable. When properly adjusted the tension exerted by the spring is supposed to just about counterbalance the weight of the door that is being transferred from the vertical section to the horizontal section of the railings. This is accomplished because, as the door travels downward the cable turns the rotatable shaft and in doing so winds the coiled spring mounted upon the shaft into a tighter configuration thereby producing an even greater upward counterbalancing effect on the weight of the door.
In original installation of the doors, when replacing broken springs, and even during periodic maintaince, it is necessary to adjust the tension of the coil springs to the desired degree so that the door can close and counterbalance almost the entire weight of the door during the raising and lowering of the door. To adjust the tension of the coiled spring it is necessary for one to loosen the releasably fixed end of the coil spring that is attached to the rotatable shaft and rotate the end of the spring relative to the shaft, either in a manner to lessen the tension or to tighten the tension. The coiled springs used in such installations are not insubstantial in the force and/or torque that they exert to accomplish their task and it is therefore considered by those skilled in the art a potentially dangerous operation. When the one end of the spring attached to the rotatable shaft is loosened it must be securely held so as not to freely uncoil back to a tension free state. Such an uncoiling while a workman or other person is in the area has produced some very severe injuries.
Recognition of the problem and attempts at solving the problem are illustrated by the U.S. Pat. No. 4,253,350 granted to De Tarr.